Chapter 6: Skeletal System (Physiology) Flashcards
Bone matrix
Bone matrix
Organic: Collagen and proteoglycans (35%)
Inorganic: Hydroxapatite (65%), Ca5(PO4)3(OH)
Hydroxyapatite also referred to as “mineral” in bone
Bone cells, including stem cells found in bone
Bone cells
Osteoblasts
Osteocytes
Osteoclasts
Mesenchymal stem cells and osteochondral progenitor
Hematopoietic stem cells (and their progeny)
Bone tissue (structure and location) (woven vs. lamellar)
In woven bone, the collagen fibers are randomly oriented in many directions. Woven bone is first formed during fetal development or during the repair of a fracture. After its formation, osteoclasts break down the woven bone, and osteoblasts build new matrix. The process of removing old bone and adding new bone is called bone remodeling and is discussed in section 6.7. Woven bone is remodeled to form lamellar bone.
Lamellar bone is mature bone that is organized into thin sheets or layers approximately 3–7 micrometers (µm) thick called lamellae (lă-mel′ē). In general, the collagen fibers of one lamella lie parallel to one another, but at an angle to the collagen fibers in the adjacent lamellae. Osteocytes, within their lacunae, are arranged in layers sandwiched between lamellae.
Bone tissue (structure and location) (cortical vs. trabecular)
Cortical/Compact bone is dense, hard, and forms the protective exterior portion of all bones.
Cancellous/trabecular/spongy bone is found inside the compact bone and is very porous (full of tiny holes)
Endochondral vs. intramembranous ossification
Both methods of ossification:
First produce woven bone that is then remodeled into lamellar bone
After remodeling, the original method of formation cannot be distinguished
1) Intramembranous ossification
Takes place in connective tissue membrane
Takes place in connective tissue membranes formed from embryonic mesenchyme
Forms many skull bones, part of mandible, diaphyses of clavicles
When remodeled, indistinguishable from endochondral bone
Centers of ossification: locations in membrane where ossification begins
Fontanels: large membrane-covered spaces between developing skull bones; unossified
2) Endochondral ossification
Takes place in cartilage (bone replaces a cartilage model)
Most bones of the skeletal system are produced this way
Cartilage formation begins at end of fourth week of development
Some ossification beginning at about week eight; some does not begin until 18-20 years of age
A hyaline cartilage model of the bone is first produced by chondroblasts
Hyaline cartilage is replaced by bone
Growth in bone length and the epiphyseal plate
Growth in length occurs at the epiphyseal plate
Involves the formation of new cartilage by interstitial cartilage growth
Requires extensive chondrocyte proliferation
Closure of epiphyseal plate: epiphyseal plate is ossified becoming the epiphyseal line. Between 12 and 25 years of age
Articular cartilage: does not ossify, and persists through life
Nutrition and bone health
Calcuim
Bone remodeling and bone’s adaptation to mechanical stress (and the importance of osteocytes in this process)
Stress causes bone remodeling to:
Increase bone mass (density)
Align trabeculae with stress
Changes causes by:
Osteoblast activity
Increases with stress
Osteocytes sense mechanical stress and are believed to stimulate osteoblast activity
Major area of research at UMKC (Bone Biology group including “the other” Dr. Stern)
Bone and the regulation of calcium homeostasis (effects of PTH)
Bone is the major storage site for calcium in the body
Calcium moves into bone as osteoblasts build new bone
Calcium moves out of bone as osteoclasts break down bone
When osteoclast and osteoblast activity is balanced, the movement of calcium in and out is equal
Osteoporosis
Osteoporosis is characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures
